A small release of gas from the anus, but of a smaller quantity than that of a regular fart. One can release a series of fartlets and achieve the same rank effect as a whole fart.
Although usually meaning a small piece of excrement attached to the hairs of your arse, sometimes known as a Clingon, it can also mean someone who is a minor, smelly, unpleasant nuisance that is sometimes difficult to get rid of.